The second generation FinFet 14nm Exynos 8890 comes with an ARM Mali T880 GPU but in the future Samsung is hoping to use its own graphics. Samsung is apparently still flat out trying to replace the ARM based licensed graphics part.
Qualcomm acquired IP from ATI (a mobile GPU core called Imagination ed.) to create a foundation for what became Adreno. Apple is working on its own mobile GPU for a while now and still ends up licensing Imagination technologies for its current A9 flagship GPU.
Samsung should remember the Intel fiasco. Back in December 2009 Intel has announced that its long developing GPU project codenamed Larrabee was officiall declared "half-not bee" and then "not be." This was a costly adventure for Intel but at least it used the technology to create the first Xeon Phi cards for complex calculations. That product goes had to head against Nvidia Tesla which is another GPU based solution for compute market as well as AMD FirePro cards.
The earliest we might see Samsung GPU as a part of future Exynos might be in 2017 but we have a serious doubts that the company can make this time frame.